It is often desirable to select and apply torque to one or more fasteners, such as nuts, screws, or the like. Prior art methods, both manual and automatic, do not provide an uncomplicated mechanism that reliably limits the torque applied to a fastener to a selectable limit. For instance, "click-type" manual torque wrenches do not actually limit torque application but only provide an audible warning that the limit has been reached. As well, the useful life of automatic drivers is often limited. Automatic torque limiting devices may overheat due to friction or may become damaged due to high loads. The torque applied to each fastener by a torque driver ideally is readily adjustable to a calibrated value. Numerous prior art drivers have attempted to solve these problems.
U.S. Pat. No. 3,845,673 to Karden et al. discloses a two-speed nut runner that has a low torque clutch designed for disengagement at a predetermined, relatively low torque. A second, high torque clutch automatically takes over the transmission of torque at a lower speed and higher torque while holding the low torque clutch in a fully released position by means of a piston that is placed inside the output shaft of the nut runner.
U.S. Pat. No. 2,069,882 to W. Hall discloses a wrench for tightening a plurality of securing members that includes a plurality of rotatable spindles operable to transmit tightening forces to the securing members, and a transmission operable by a single drive to rotate the several spindles independently to tighten the members to the same degree of tightness. The transmission includes pinions associated with the spindles, and an element, rotated by the drive, operable to successively cooperate with pairs of substantially opposite pinions to partially rotate the same.
U.S. Pat. No. 2,781,682 to W. B. Herndon discloses a torque wrench with multiple spindles that provides a steady torque for setting screw-threaded fastenings while allowing the drive to slip when the fastening is tight.
U.S. Pat. No. 4,909,105 to Namiki et al. discloses an automated nut driving apparatus having a plurality of motors for rotating respective ones of a plurality of drive shafts to respective sockets holding nuts. The nut driver includes a plurality of universal joints connecting the sockets and drive shafts while allowing the sockets to be tilted with respect to the drive shafts. Universal joints are movable axially with respect to the drive shafts to allow the sockets to be retracted under reactive forces produced when the nuts engage the wheel attachment bolts.
U.S. Pat. No. 5,092,410 to Wallace et al. discloses a hydraulic torque impulse generator using a dual piston arrangement to provide impacts to a rotatable anvil. Automatic shut-off and control apparatus is provided for limiting the pressure without reversing the direction of the driving clutch cage. A pressure venting arrangement permits one impact per revolution.
U.S. Pat. No. 4,533,337 to K. C. Schoeps discloses a hydraulic torque impulse tool having a power inertia drive member, a hydraulic fluid chamber, and a cam driven piston in the fluid chamber for reciprocating movement.
U.S. Pat. No. 5,125,298 to C. O. Smith discloses an automatic wheel assembly line in which an array of fastener members is prepared, corresponding in number and geometric pattern to the array of coacting fastener members on the vehicle hub and to the array of bolt holes on the wheel assembly. The assembly includes a source of fasteners, a feeder mechanism having an outboard face, means defining a plurality of fastener receptacles, means operative to transport fasteners and means to move the loaded fasteners.
U.S. Pat. No. 4,989,478 to Trivedi et al. discloses an apparatus for tightening or loosening a plurality of bolts or other rotatable elements in which a drive socket and a pair of reaction sockets are supported by an elongated beam member.
U.S. Pat. No. 3,905,254 to Palatnick et al. discloses a tool for loosening and removing the lug nuts of an automobile and truck wheels with selectively positioned non-rotating stabilized sockets.
As can be understood from a review of the background as discussed above, there remains the need for an improved torque control mechanism that offers a selectable, calibrated control over torque applied to one or more fasteners, a simplified power driver construction that allows for hand-held operation, a long-life gear configuration, and a driver which may be produced at reduced levels of capital investment. Those skilled in the art will appreciate that the present invention provides solutions to these and other problems.